This invention pertains to finger operated switching devices and more particularly to such devices which utilize magnets to provide the restoring forces after operation of the switching device.
Finger operated switching devices have many uses such as in key-operated office machines, entry tabulators, key punchers and calculators, keyboards in electric typewriters, word processors, printing and typesetting machines and keysets in telephones. In each of these applications a key assemblage is momentarily depressed by a finger from a home position to an active position to close a circuit, and upon release of the finger the key assemblage is restored to its home position and the circuit opens. In many of the devices, mechanical biasing means biased the key assemblage to the home position so that upon release the key assemblage automatically leaves the active position. It is known to use springs and weights for the biasing means. However, such solutions only add further complications. First they require extra moving parts and secondly they introduce an undesirable force vs. displacement characteristic to the key assemblage. In particular such means have a characteristic where the opposing force monotonically increases with displacement. This monotonic increase creates two problems. First, because the restoring force increases with increasing displacement, it is less likely that the necessary throw or travel of the key assemblage for the desired switching function will occur for each user. Secondly, it has been found that users of typewriters or similar devices have become accustomed to a particular force vs. displacement characteristic which generally increases to a maximum opposing force for an intermediate displacement and thereafter rapidly falls off to a lesser opposing force. This phenomenon is known as tactile feel or snap action. If the operator does not sense such tactile feel, his physiological feedback is disturbed and keystroking is slowed down and/or becomes erratic and unreliable. There have been many proposals to simulate tactile feel by adding mechanical means such as toggle devices. However, such devices merely add complexity and more moving parts to the devices.
Another proposal is shown in U.S. Pat. No. 3,815,006 wherein magnetic means are used to provide the tactile feel. However, the device shown therein uses moving sets of magnets to provide the tactile feel or over-center-or snap action, and other magnets or springs to provide the means for the automatic return of the key. Again while tactile feel is provided it is at the expense of simplicity and restriction to the use of single keys as opposed the arrays of keys.
It is accordingly a general object of the invention to provide an improved finger operated switching device having a minimum number of moving parts.
It is a further object of the invention to provide such a device wherein the biasing or restoring forces are provided by non-mechanical means and simulate the desired tactile feel.
In an attempt to make a finger operated switching device requiring a minimum of moving parts it is necessary to consider the electrical switch portion per se. Generally the switch portion comprises contact sets which are mechanically engaged or disengaged in response to the travel of the key assemblage. While such contact sets perform adequately they introduce parts which are subject to wear.
It is accordingly an object of a feature of the invention to provide an electrical switch portion which does not have parts which are subject to contact wear.
Finally, with some switching devices it is desirable to have key assemblages which are locked in an activated position even after release of the finger, and are only released at some later time by the operation of another key assemblage or other device. The most immediate examples are the shift lock key of a typewriter and the extension and line selection buttons of telephone handsets.
It is accordingly an object of and a further feature of the invention to provide such a switching device which is extremely simple and less complex than previously available devices.